Process for hydroconversion of paraffin containing feeds

ABSTRACT

Hydroconversion of paraffin containing hydrocarbon feeds is effected over a supported Group VIII and Group VI metal containing catalyst also containing a hydrocracking suppressant such as a Group IB metal, wherein the catalyst is preferably prepared by fixing the Group IB metal on to the support prior to incorporating the Group VI metal on to the support.

FIELD OF THE INVENTION

This invention relates to a non-noble metal catalyst for thehydroconversion of paraffin containing feedstocks. More particularly,this invention relates to a catalyst containing cobalt or nickel, aGroup VI metal and a Group IB metal, and the use of that catalyst forhydroisomerizing waxy feedstocks, particularly waxy feedstocks producedby a hydrocarbon synthesis reaction, e.g., the Fischer-Tropsch process.

BACKGROUND OF THE INVENTION

The use of supported Group VIII metals in hydroconversion processes iswell known. Often, these metals are combined with Group VIA metals,e.g., cobalt and molybdenum, on suitable supports for use inhydroconversion processes. Group VIII noble metals, e.g., platinum andpalladium, are efficient hydroconversion catalysts, but these metals arealso relatively expensive. Consequently, there exists a desire to findnon-noble metals or combinations thereof that can provide activity,selectivity, and activity maintenance equivalent to that of noblemetals, thereby significantly lowering catalyst costs.

Unfortunately, however, hydroconversion catalysts comprising Group VIIInon-noble metals are prone to undergo undesirable hydrogenolysis.Consequently, the hydrogenolysis, e.g., hydrocracking, producessignificant amounts of gaseous products e.g., methane. A catalyst,therefore, that can eliminate or substantially reduce the hydrogenolysisaspect of the process can be more efficient and more economic because ofincreased yields of desired products and decreased yields of undesirablegaseous products.

SUMMARY OF THE INVENTION

In accordance with this invention, a new bi-functional catalyst for thehydroconversion of hydrocarbons, particularly waxy hydrocarbons fromFischer-Tropsch hydrocarbon synthesis processes, is provided andcomprises a non-noble Group VIII metal in conjunction with a Group VIand a Group IB metal supported on an acidic component.

The presence of the Group IB metal is believed to mitigate the excessivehydrogenolysis and cracking activity of Group VIII metals e.g., cobaltwhich produce excessive amounts of undesirable methane and other C₄ ⁻gases. Thus, the bifunctionality of hydrogenation and isomerization ismaximized while hydrogenolysis and cracking activity is minimized. Thepreferred metals are Group VIII non-noble metals, preferably cobalt, inconjunction with a Group VI metal, preferably molybdenum, and a Group IBmetal, preferably copper.

Hydrocracking suppression can be effectively measured by suppressingmethane, since hydrocracking most easily occurs through terminalcracking. The process is conducted with hydrocarbon containing feeds atusual hydroisomerization conditions. Generally, the process of thisinvention will lead to methane yields of less than about 10 wt % basedon total 700° F.+ conversion, preferably less than about 6 wt %, morepreferably less than about 1 wt %, and still more preferably less thanabout 0.1 wt %.

Typical hydroisomerization conditions are well known in the literatureand can vary widely. For example, broad and preferred ranges for theseconditions are shown in the following table:

    ______________________________________                                        CONDITION    BROAD         PREFERRED                                          ______________________________________                                        Temperature, °F. (°C.)                                                       300-900(149-482° C.)                                                                 550-750(288-399° C.)                        Total pressure, psig                                                                        0-2500        300-1200                                          Hydrogen Treat Rate,                                                                       500-5000      2000-4000                                          SCF/B                                                                         Hydrogen Consumption                                                                       50-500        100-300                                            Rate, SCF/B                                                                   ______________________________________                                    

The catalysts useful in this invention preferably contain an acidfunction as well as the hydrocracking suppressant. The hydrocrackingsuppressant may be a Group IB metal, preferably copper, in amountseffective to reduce hydrogenolysis, e.g., at least about 0.1 wt %,preferably about 0.1-10 wt %, more preferably about 0. 1-5 wt %, stillmore preferably about 0.1-2 wt % based on catalyst.

The Group VIII non-noble metals may include cobalt, nickel, or iron,preferably iron, cobalt or nickel, more preferably cobalt. The GroupVIII metal is usually present in catalytically effective amounts, thatis, ranging from 0.5 to 5 wt %. Preferably, a Group VI metal isincorporated into the catalyst, e.g., molybdenum, in effective catalyticamounts of about 1-20 wt %.

The acid functionality can be furnished by a support with which thecatalytic metal or metals can be incorporated or deposited by well knownmethods. The support can be any refractory oxide or mixture ofrefractory oxides or zeolites or mixtures thereof. Preferred supportsinclude silica, alumina, silica-alumina, silica-alumina-phosphates,titania, zirconia, vanadia and other Group III, IV, V or VI oxides, aswell as Y sieves, such as ultra stable Y sieves. Preferred supportsinclude alumina and amorphous silica-alumina, more preferably amorphoussilica-alumina where the silica concentration of the bulk support isless than about 50 wt %, preferably less than about 35 wt %, morepreferably 15-30 wt %. When alumina is used as the support, smallamounts of chlorine or fluorine may be incorporated into the support toprovide the acid functionality.

A preferred supported catalyst has surface areas in the range of about180-400 m² /gm, preferably 230-350 m² /gm, and a pore volume of lessthan 1.0 ml/gm, preferably 0.3 to less than 1.0 ml/gm, a bulk density ofabout 0. 5-1.0 g/ml, and a side crushing strength of about 0.8 to 3.5kg/mm.

The preparation of preferred amorphous silica-alumina microspheres foruse as supports is described in Ryland, Lloyd B., Tamele, M. W., andWilson, J. N., Cracking Catalysts, Catalysis; Volume VII, Ed. Paul H.Emmett, Reinhold Publishing Corporation, New York, 1960.

During hydroisomerization, the 700° F.+ conversion to 700° F.- on a oncethrough basis ranges from about 20-80%, preferably 30-70%, morepreferably about 40-60%; and essentially all olefins and oxygenatedproducts are hydrogenated.

The feed can be any hydrocarbon containing material having a finalboiling point of up to about 1050° F. (566° C.). A particularlypreferred feed is a C₅ + material derived from a hydrocarbon synthesis,e.g., Fischer-Tropsch process, preferably a non-shifting process asexemplified in U.S. Pat. No. 4,568,663 and EP 450860.

The feed materials for hydroisomerization are typically comprised ofwaxy feeds, e.g., C₅ +, a portion of which and preferably at least about50 wt % of which boils above about 350° F. (177° C.), preferably aboveabout 550° F. (288° C.), and most preferably contain substantiallynormal paraffins obtained from a Fischer-Tropsch process or as obtainedfrom slack waxes. Slack waxes are the by-products of lube dewaxingoperations where a diluent such as propane or a ketone (e.g.,methylethyl ketone, methylisobutyl ketone) or other diluent is employedto promote wax crystal growth, the wax being removed from the lube baseoil by filtration or other suitable means. The slack waxes are generallyparaffinic in nature, boil above about 600° F. (315° C.), preferably inthe range of 600° F. to 1050° F. (315°-566° C.) and may contain fromabout 1 to about 35 wt % oil. Waxes with lower oil contents, e.g., 5-20wt % are preferred; however, waxy distillates or raffinates containing5-45% wax may also be used as feeds. Slack waxes are usually freed ofpolynuclear aromatics and heteroatom compounds by techniques known inthe art; e.g., mild hydrotreating as described in U.S. Pat. No.4,900,707, which also reduces sulfur and nitrogen levels. Feeds whichcontain high levels of sulfur, e.g., >30 ppm sulfur, may also be used asthe catalyst described here is sulfur tolerant. In addition, feeds suchas gas field condensates may be used as feeds or other petroleum derivedfeeds with high sulfur levels that require hydroisomerization to improveits properties.

A distillation showing the fractional make up (±b 10 wt % for eachfraction) for a typical Fischer-Tropsch process feed stock follows:

    ______________________________________                                        Boiling Temperature Ranges                                                                      Wt % of Fraction                                            ______________________________________                                        IBP-320° F. (160° C.)                                                             13                                                          320-500° F. (160-260° C.)                                                         23                                                          500-700° F. (260-371° C.)                                                         19                                                          700-1050° F. (371-566° C.)                                                        34                                                          1050° F.+ (566° C.+)                                                              11                                                          Total             100                                                         ______________________________________                                    

Feeds derived from Fischer-Tropsch processes are essentially free ofsulfur but may have some oxygenated products incorporated therein.

The feed may be treated or untreated as regarding the removal ofhetero-atoms containing compounds (e.g., sulfur and oxygen containingcompounds). However, when the feed is treated, essentially all of thesulfur and oxygen should be reduced to sulfur levels of less than about10 wppm, preferably less than 2 ppm sulfur, more preferably less than 1wppm sulfur, and oxygen levels of less than about 10 wppm. Such feedsare most preferably characterized by the substantial absence of sulfurand oxygen. Hydrotreating is effected by any of the well knownhydrotreating (e.g., hydrodesulfurization) processes known in theliterature.

The catalyst can be prepared by any well known method, e.g.,impregnation with an aqueous salt, incipient wetness technique, followedby drying at about 125°-150° C. for 1-24 hours, calcination at about300°-500° C. for about 1-6 followed by reduction with a hydrogen or ahydrogen containing gas.

In the preparation of bi-metallic catalysts, such as catalystscontaining cobalt and molybdenum, the order in which the metals aredeposited upon, or composited with, or incorporated into, the supportdoes not generally affect the performance of the catalyst. Thus, whethercobalt is added to the support before the molybdenum is added to thesupport, or if the cobalt and molybdenum are added to the supportsimultaneously, e.g., co-impregnation, makes little difference incatalyst performance.

Nevertheless, the order of metal addition for the tri-metallic catalystsdescribed herein can affect the hydroisomerization performance of thecatalyst insofar as hydrogenolysis and conversion to branched species isconcerned. Thus, improved catalytic performance occurs when the Group IBmetal, e.g., copper, the hydrogenolysis suppressant, is fixed onto thesupport prior to incorporation of the Group VI metal, e.g., molybdenum.Fixing the metal onto the support, for purposes of this specification,means that the metal, incorporated as a decomposable compound,preferably a decomposable metal salt, has been converted to the metaloxide, usually and typically by calcination at elevated temperatures inthe presence of an oxygen containing gas, e.g., air, for a timesufficient to convert substantially all and preferably all, of the metalcompound to the oxide.

The cobalt may be incorporated or fixed onto the support either before,after, and preferably simultaneously, e.g., co-impregnation, with thecopper, so long as the molybdenum is incorporated and fixed onto thesupport after fixing of the copper on to the support.

The reason for the difference in catalyst performance is not wellunderstood at this time; suffice to say that the performance differencedoes exist.

Upon fixing of the molybdenum onto the support, i.e., after the lastcalcination, the metal oxides are activated by treating the compositedsupport with hydrogen or a hydrogen containing gas, which effectivelyreduces the metal to its elemental form. Reduction need only be for thatperiod of time sufficient to produce an effective hydroisomerizationcatalyst with hydrogenolysis suppression activity. Generally, at leastabout 50% of the metal oxides are reduced, preferably at least about80%, more preferably at least about 90% reduction is effected.

The following examples will serve to illustrate, but not limit thisinvention.

EXAMPLE 1

A commercial Co--Mo catalyst on a SiO₂ --Al₂ O₃ support containing 20-30wt % bulk silica was reduced at 370° C. for 3 hours in hydrogen. Thecatalyst was used to hydroisomerize n-heptane as a model compoundrepresenting the more refractory paraffins present in Fischer-Tropschliquids. The catalyst contains 3.2 wt. % CoO, 15.2 wt. % MoO₃, and 15.5wt. % SiO₂. The balance of the material is Al₂ O₃ with some impurities.Surface area is 266 m2/g, pore volume (measured by Hg porosimetry) is0.63 ml/g, and the compacted bulk density is 0.67 g/ml. The results ofthe isomerization test are presented in Table 1.

EXAMPLE 2

The Co--Mo catalyst of Example 1 was impregnated with an aqueoussolution of copper nitrate to introduce 0.5 wt % Cu. A description ofthe preparation follows. 11.582 g of Cupric Nitrate (Fisher Lot #951352)was dissolved in deionized water to make up a total volume of 480 mL. Arotary impregnation vessel was then used to impregnate the CopperNitrate solution onto 615.0 g of the commercial Co--Mo catalystdescribed in Example 1. Since this catalyst had a non-volatile contentof 98.6 wt. %, this amount of catalyst represented 606.4 g dry solids.The wet impregnated material was air dried overnight and then dried in aforced air oven for 4 hours at 120° C. The dried catalyst was thencalcined in a muffle furnace with flowing air for 2 hours at 427° C.

The catalyst was calcined in air at 370° C. and reduced in hydrogen at370° C. for 3 hours. The Co--Mo--Cu catalyst was used to hydroisomerizen-heptane. The results are presented in Table 1.

The catalyst of Example 1, while active for hydroisomerization, hasextremely high hydrocracking activity as evidenced by very high methaneand n-butane yields and the destruction of normal and iso-heptanes.Liquid yield is decreased to a value <70 wt %.

The catalyst of this invention, Co--Mo--Cu, the catalyst of Example 2,is the preferred hydroisomerization catalyst on the basis of higherselectivity to isomerized product and substantially decreasedhydrocracking activity. The yield of liquid product exceeds 92 wt %, andthe formation of iso-heptanes is roughly 35% greater than that ofExample 1.

                  TABLE 1                                                         ______________________________________                                        ISOMERIZATION OF HEPTANE WITH                                                 Co--Mo AND Co--Mo--Cu CATALYSTS                                               n-Heptane, 425° C., 100 psig, 5 W/H/W, H.sub.2 /Oil = 6                             EXAMPLE                                                                       1      2                                                                      Catalyst                                                                      Co--Mo Co--Mo/Cu                                                 ______________________________________                                        C.sub.1        17.7     7.7                                                   i-C.sub.4      0.9      0.9                                                   n-C.sub.4      8.8      5.1                                                   n-C.sub.7      27.5     43.7                                                  2-Me-Hex       3.6      7.4                                                   3-Me-Hex       4.6      9.1                                                   i-C.sub.7 's   8.2      16.5                                                  ______________________________________                                    

To determine the effect of order of metal addition or the performance ofCo--Cu--Mo catalysts, several catalysts were prepared.

EXAMPLE 3

This example describes a catalyst where the Cu and Co were added to thecarrier before Mo addition: 1.910 g of Cupric Nitrate (Fisher Lot#951352) and 12.840 g of Cobalt Nitrate (Mallinckrodt Lot #3420 KEMD)were added to an Erlenmeyer flask and dissolved in deionized water to atotal volume of 78.6 ml. To the Erlenmeyer flask was added 85.474 g ofSiO₂ --Al₂ O₃ support (with a dry solids content of 95.0 wt. %). Theflask was shaken until all the particles were wet. The carrier contained19.0 wt. % SiO₂ and the balance Al₂ O₃. The surface area was 326 m² /gand the pore volume (measured by Hg porosimetry) was 0.77 ml/g. Aftershaking the flask to make sure all the particles were wet, the wetmaterial was dried in air overnight. The material was then dried in aforced air oven for 4 hours at 120° C. and then calcined in a mufflefurnace in flowing air for 2 hours at 427° C.

17.803 g of Ammonium Heptamolybdate (Mallinckrodt Lot #3420 KPAM) wasadded to 13.47 g of Ammonium Hydroxide (Mallinckrodt 30 wt. % NH₃ Lot#1177 KPLA) in an Erlenmeyer flask. To this mixture was added deionizedwater to a total volume of 74.4 ml. The Cu--Co containing carrier wasthen added to this solution and the flask shaken until all the particleswere wet. This material was then dried in air overnight and then driedin a forced air oven for 4 hours at 120° C. The Cu--Co--Mo catalyst wasthen calcined in a muffle furnace with flowing air for 2 hours at 427°C.

EXAMPLE 4

This example describes a catalyst with only Cu and Co. 1.910 g of CupricNitrate (Fisher Lot #951352) and 12.840 g of Cobalt Nitrate(Mallinckrodt Lot #4544 KEMD) were added to an Erlenmeyer flask anddissolved in deionized water to a total volume of 78.6 ml. To theErlenmeyer flask was added 85.474 g of SiO₂ --Al₂ O₃ support (with a drysolids content of 95.0 wt. %). The flask was shaken until all theparticles were wet. The carrier contained 19.0 wt. % SiO₂ and thebalance Al₂ O₃. The surface area was 326 m² /g and the pore volume(measured by Hg porosimetry) was 0.77 ml/g. After shaking the flask tomake sure all the particles were wet, the wet material was dried in airovernight. The material was then dried in a forced air oven for 4 hoursat 120° C. and then calcined in a muffle furnace in flowing air for 2hours at 427° C.

EXAMPLE 5

This example describes a catalyst where the Mo was added first to thecarrier before the Co and Cu. 18.902 g of Ammonium Heptamolybdate(Mallinckrodt Lot 3420 KPAM) was placed in an Erlenmeyer flask anddissolved with deionized water to a total volume of 80.7 ml. To theErlenmeyer flask was added 84.06 g of SiO₂ --Al₂ O₃ support (with a drysolids content of 96.6 wt. %). The flask was shaken until all theparticles were wet. The carrier contained 19.0 wt. % SiO₂ and thebalance Al₂ O₃. The surface area was 326 m2/g and the pore volume(measured by Hg porosimetry) was 0.77 ml/g. This material was then driedin air overnight and then dried in a forced air oven for 4 hours at 120°C. The Mo-containing carrier was then calcined in a muffle furnace withflowing air for 2 hours at 427° C.

1.812 g of Cupric Nitrate (Fisher Lot #951352) and 12.172 g of CobaltNitrate (Mallinckrodt Lot #4544 KEMD) were placed in an Erlenmeyer flaskand dissolved into deionized water to a total volume of 69.3 ml. To theErlenmeyer flask was added 91.12 g of the Mo-containing carrier. Theflask was shaken until all the particles were wet. After shaking theflask to make sure all the particles were wet, the wet material wasdried in air overnight. The material was then dried in a forced air ovenfor 4 hours at 120° C. and then calcined in a muffle furnace in flowingair for 2 hours at 427° C.

EXAMPLE 6

This example describes a catalyst where the Cu was added in a post-treatafter the Mo and Co had each been added to the carrier. 18.902 g ofAmmonium Heptamolybdate (Mallinckrodt Lot #3420 KPAM) was placed in anErlenmeyer flask and dissolved with deionized water to a total volume of80.7 ml. The 19.0 wt. % SiO₂ /Al₂ O₃ carrier (with a dry solids contentof 96.6 wt%) described in Example 3 was then added to this solution andthe flask shaken until all the particles were wet. This material wasthen dried in air overnight and then dried in a forced air oven for 4hours at 120° C. The Mo-containing carrier was then calcined in a mufflefurnace with flowing air for 2 hours at 427° C.

12.172 g of Cobalt Nitrate (Mallinckrodt Lot #4544 KEMD) was placed inan Erlenmeyer flask and dissolved in deionized water to a total volumeof 69.2 ml. To the Erlenmeyer flask was added 91.04 g of theMo-containing carrier. The flask was shaken until all the particles werewet. After shaking the flask to make sure all the particles were wet,the wet material was dried in air overnight. The material was then driedin a forced air oven for 4 hours at 120° C. and then calcined in amuffle furnace in flowing air for 2 hours at 427° C.

1.472 g of Cupric Nitrate (Fisher Lot #951352) was placed in anErlenmeyer flask and dissolved in deionized water to a total volume of61.6 ml. To the Erlenmeyer flask was added 77.0 g of theMo-Co-containing carrier. The flask was shaken until all the particleswere wet. After shaking the flask to make sure all the particles werewet, the wet material was dried in air overnight. The material was thendried in a forced air oven for 4 hours at 120° C. and then calcined in amuffle furnace in flowing air for 2 hours at 427° C.

The catalysts from Examples 3-6 representing different methods ofsynthesis of the catalyst of this invention were tested in heptaneisomerization, and the results are presented in Table 2.

                  TABLE 2                                                         ______________________________________                                        ISOMERIZATION OF HEPTANE WITH                                                 Co--Mo--Cu CATALYSTS                                                          n-Heptane, 425° C., 100 psig, 5 W/H/W, H.sub.2 /Oil =6                 EXAMPLE                                                                       3              4        5          6                                          Catalyst                                                                      Cu--Co/Mo      Cu--Co   Mo/Co--Cu  Mo/Co/Cu                                   ______________________________________                                        C.sub.1 6.3        2.9      10.1     12.1                                     i-C.sub.4                                                                             0.8        0.3      0.7      0.8                                      n-C.sub.4                                                                             5.2        0.8      4.7      5.1                                      n-C.sub.7                                                                             43.7       82.2     44.7     42.2                                     2-Me-Hex                                                                              8.0        3.0      6.6      6.0                                      3-Me-Hex                                                                              9.8        4.2      8.2      7.4                                      i-C.sub.7 's                                                                          17.8       7.2      14.7     13.4                                     ______________________________________                                    

Example 3 representing the preferred synthesis method provides anisomerization catalyst with low cracking activity coupled with highisomerization activity as indicated by the methane and iso-heptaneyields. Example 4 illustrates that Mo is an essential catalystingredient. In the absence of Mo the catalyst has poor activity of anytype. Examples 5 and 6 demonstrate that catalyst synthesis based on theinitial deposition of Mo followed by the addition of Cu and Co producesinferior catalysts characterized by high methane yields indicative ofhigh cracking activity and decreased yields of the desired iso-heptanes.

What is claimed is:
 1. A process for isomerizing a feed containing C₅ +paraffins comprising passing the feed, at effective isomerizationconditions of temperatures and pressures over a non-noble metal,supported catalyst in the presence of hydrogen, the catalyst comprisinga Group VIII metal, a Group VI metal, and an effective amount of a GroupIB metal as a hydrogenolysis suppressant and wherein the Group IB metalis fixed on the support prior to incorporation of the Group VI metal onthe support.
 2. The process of claim 1 wherein the feed containsparaffins boiling above about 350° F.
 3. The process of claim 2 whereinthe Group VIII metal is cobalt, the Group VI metal is molybdenum, theGroup IB metal is copper, and the support is a refractory oxide.
 4. Theprocess of claim 3 wherein conversion of the feed ranges from about20-80%.
 5. The process of claim 4 wherein the methane yield is less than10 wt %.
 6. The process of claim 3 wherein cobalt and copper aresimultaneously incorporated on the support.
 7. The process of claim 3wherein the support is silica-alumina with a silica content of less thanabout 50 wt %.
 8. The process of claim 3 wherein the feed issubstantially sulfur free.
 9. The process of claim 8 wherein the feed isderived from a Fischer-Tropsch hydrocarbon synthesis process.
 10. Theprocess of claim 3 wherein cobalt is present on the catalyst in anamount of 0.05-5 wt %.
 11. The process of claim 10 wherein molybdenum ispresent on the catalyst in an amount of 1-20 wt %.
 12. The process ofclaim 11 wherein copper is present on the catalyst in an amount of atleast about 0.1 wt %.
 13. The process of claim 12 wherein copper ispresent on the catalyst in an amount of 0.1-5 wt %.